Study of the neoformed phases formed during the spent nuclear fuel alteration in groundwater

The final disposal of spent nuclear fuel in geological repository requires to understand its alteration and to determine the formation of secondary phases than can form at the interface between UO2+x and the solution at the equilibrium with the media. These nanometer-thick phases are complex to characterize by solution analysis and difficult to characterize since realistic flat surface at large scale is difficult to obtain after long term alteration by groundwater with UO2+x. The aim of this proposal is to use the direct proof of concept (Lu et al, submitted) to determine on absolute scale the reflectivity as well as the scattering produced by a dense packing of micron-sized grains. Thus, a combination of SAXS and WAXS will allow for the first time to in situ characterize the thickness of these neoformed phases using the reflectivity signal, the nanoporosity of the layer and the crystalline structure of these phases from the scattering signals at higher q on isolated grains.